The present invention relates to a method of writing any fine patterns on a resist by an electron beam exposure and an electron beam exposure system.
In recent years, a high throughput has been required in manufacturing semiconductor devices, for example, in a lithography processes for writing fine patterns on a semiconductor wafer. The lithography may be classified into a photo-lithography using an ultraviolet ray, an X-ray lithography using an X-ray and an electron beam lithography using an electron beam. The electron beam lithography is carried out by use of a mask having a desired pattern. This electron beam lithography using the mask is often applied to regularly repeated patterns comprising a large number of repeated unit patterns, for example, memory cell patterns such as dynamic random access memory and static random access memory. In the meantime, a variable shaped electron beam exposure is applied to random patterns to form peripheral circuit regions.
FIG. 1 is a plane view illustrative of the regularly repeated patterns 11 formed in a first region 2 and the random patterns 4 formed in a second region 3. The regularly repeated patterns 11 and the random patterns 4 are bounded by pattern boundary portions 18. The regularly repeated patterns 11 are formed by an electron beam exposure using a mask. The random patterns 4 are formed by the variable shaped electron beam exposure. Prior to the variable shaped electron beam exposure, a pattern size calibration is conducted to decide a beam size of a variable shaped electron beam. Actually, however, there is an error on the beam size of the variable shaped electron beam. This error on the beam size of the variable shaped electron beam causes a dimensional variation or a size variation of the random pattern. This results in a difference in size or dimension of a resist between the regularly repeated patterns 19 and the random patterns 20. FIG. 2 is a fragmentary enlarged plane view illustrative of a difference in size or dimension of a resist between the regularly repeated patterns 19 and the random patterns 20 obtained after exposure and development.
In order to solve this problem, it is necessary to re-size the variable shaped electron beam so that the size of the random patterns 20 is reduced to correspond to the size of the regularly repeated patterns 19 in a direction along a boundary line between the individual pairs of the regularly repeated patterns 19 and the random patterns 20.
FIG. 3 is a fragmentary schematic view illustrative of a conventional variable shaped electron beam exposure system. The conventional variable shaped electron beam exposure system has an electron gun emitting an electron beam 22, a first aperture 23, a deflector 25 and a second aperture 24. The electron beam emitted from the electron gun is partially transmitted through the first aperture to shape the electron beam. This shaped electron beam is then deflected by the deflector 25 so that the shaped electron beam is partially transmitted through the second aperture to re-shape the electron beam. The shape of the electron beam having been transmitted through the second aperture 24 is variable by controlling the deflection by the deflector 25. As a result, a variable shaped electron beam 21 is obtained. FIG. 4 is a plane view illustrative of a relationship between a shape of the electron beam and the first and second apertures 23 and 24, wherein the electron beam is re-sized by a size shift amount 26. If the electron beam is re-sized by a size shift amount 26 by controlling the deflection by the deflector 25, then an origin 8 of a variable shaped electron beam shot remains fixed in position. FIG. 5 is a fragmentary enlarged plane view illustrative of the regularly repeated patterns 19 and the random 20 written by the resized variable shaped electron beam. The regularly repeated patterns 19 are formed in the first region such as memory cell region whilst the random patterns 20 are formed by the second region such as the peripheral region which is bounded by a boundary line 18 from the first region. The variable shaped electron beam is re-sized so that the individual random patterns 20 are re-sized by the size shift amount 26 but only on a first side 27 thereof, whilst a second side 28 opposite to the first side 27 remains fixed, wherein the origin of the variable shaped electron beam shot is on the second side 28. By adjusting the deflection of the electron beam by the deflector 25, it is possible to have the first side 27 of the individual random pattern 20 aligned to or correspond to the individual regularly repeated pattern 19. However, it is impossible for the above conventional method to have the second side 28 of the individual random pattern 20 aligned or correspond to the regularly repeated pattern 19. In order to have the second side 28 of the individual random pattern 20 aligned or correspond to the regularly repeated pattern 19, it is required to uniformly off-set on both sides of the individual random pattern 20 by utilizing overlay exposures. In this case, however, positioning relative to base patterns 7 depends upon individual patterns. This means that it is impossible to align the random patterns 20 to the regularly repeated patterns 19 in consideration of the random patterns 20 only. As a result, the accuracy of alignment is deteriorated.
If the above variable shaped electron beam exposure is applied to the formation of logic devices, then it is necessary to conduct calibrations in size of the variable shaped electron beam for every logic devices having different sizes. Further, it is also necessary to conduct a pilot writing for obtaining optimum exposure conditions to realize the desired pattern size of the resist. For these reasons, it takes a few hours to conduct the electron beam lithography.
In addition, a size shift from the design size appears in etching process. Thus, it is necessary to estimate the size shift in the etching process. This estimation is needed for every products or devices different in design size, base material, structure and thickness of layers or films. This results in a further extended time necessary for the electron beam lithography.
Moreover, the conventional variable shaped electron beam exposure system is engaged with a problem with deterioration in accuracy of the resist pattern size due to displacement of the paired first and second apertures and a variation in voltage applied to the deflector 25. If particularly contact patterns are written, rectangular-shaped fine patterns designed in accordance with fine design rules are written by the variable shaped electron beam. In this case, the variation in size of the resist pattern obtained becomes more remarkable.
In recent years, as having responded to the requirements for increase in variety of the logic devices and production in a small scale, it is required to shorten the time necessary for the manufacturing the logic devices. It is required to eliminate the process which provides a bar to shorten the time necessary for the manufacturing the logic devices.
As the integration of the devices and scaling down thereof have been promoting, there is needed, in a contact writing process applied with the minimum design rule, an extremely high accuracy in size of the resist pattern within a range of variation from -10% to +10% of the design size, for example, within 0.03 micrometers.
It is essential to solve the issue with deteriorated accuracy in size of the resist patterns written by the variable shaped electron beam exposure.